Process for the partial combustion of hydrocarbonaceous fuels to produce substantially soot-free gases

ABSTRACT

The soot content of a hydrogen and carbon monoxide-containing gas mixture obtained by the partial combustion of a hydrocarbonaceous fuel is substantially reduced by passing the partially-combusted gases through a soot-conversion zone maintained at an elevated temperature and pressure, and retarding the passage of soot particles through the zone for a sufficient period of time that the soot is substantially converted to carbon monoxide. An apparatus suitable for effecting soot-conversion is also disclosed.

Unite States Patent 1191 Van Lookeren Campagne [111 3,868,331 [451 Feb.25, 1975 PROCESS FOR THE PARTIAL COMBUSTION OF HYDROCARBONACEOUS FUELSTO PRODUCE SUBSTANTIALLY SOOT-FREE GASES [75] Inventor: Nicolaas VanLookeren Campagne,

Rotterdam, Netherlands [73] Assignee: Shell Oil Company, New York, N.Y.22 Filed: June 18, 1973 [21] App]. No.: 370,996

[30] Foreign Application Priority Data June 26, 1972 Great Britain29768/72 [52] US. Cl. 252/373, 48/196 R, 48/197 R, 48/202, 48/206,48/212, 48/215, 48/95 [51] Int. Cl ..C01b 2/14 [58] Field of Search48/99, 102 R, 63, 89, 105, 48/107, 95,197 R, 211, 212, 213, 215,196

[56] References Cited UNITED STATES PATENTS 408,674 8/1889 Rose 48/632,605,178 7/1952 Hemminger 48/215 2,709,646 5/1955 Haug 48/211 OXYGEN2,779,667 1/1957 Keith 48/196 2,844,452 7/1958 48/196 3,042,507 7/196248/215 3,048,481 8/1962 Eastman 48/206 3,536,455 10/1970 Bogdandy et al.23/281 3,607,154 9/1971 White et a1. 48/102 R 3,682,605 8/1972 Wada48/107 3,715,301 2/1973 Tassoney et al. 208/8 FOREIGN PATENTS ORAPPLICATIONS 1,165,440 10/1969 Great Britain 48/215 734,222 7/1955 GreatBritain 48/212 Primary ExaminerS. Leon Bashore Assistant ExaminerPeterF. Kratz Attorney, Agent, or FirmA. A. .lecminek [57] ABSTRACT The sootcontent of a hydrogen and carbon monoxidecontaining gas mixture obtainedby the partial combustion of a hydrocarbonaceous fuel is substantiallyreduced by passing the partially-combusted gases through asoot-conversion zone maintained at an elevated temperature and pressure,and retarding the passage of soot particles through the zone for asufficient period of time that the soot is substantially converted tocarbon monoxide. An apparatus suitable for effecting soot-conversion isalso disclosed.

10 Claims, 2 Drawing Figures COOLED GASES PATENTEDFEB 25' I975 F/GlOXYGEN COOLED GASES PROCESS FOR THE PARTIAL COMBUSTION OFI-IYDROCARBONACEOUS FUELS TO PRODUCE SUBSTANTIALLY SOOT-FREE GASESBACKGROUND OF THE INVENTION The present invention relates to a processand an apparatus for the partial combustion of hydrocarbonaceous fuelsto produce gases having a substantially reduced soot content.

The gases produced by processes for the partial combustion ofhydrocarbonaceous fuels invariably contain a substantial amount of freecarbon (i.e., soot) which is undesirable for the subsequent utilizationor processing of the gases and which should therefore be removed. Theremoval of the soot is normally achieved by scrubbing the gases withwater. The resulting dispersion of soot particles in water is thenprocessed in order to recover substantially soot-free water and soot.The soot removal facilities are expensive and the recovered sootgenerally has a low value. It is therefore an object of the presentinvention to provide a process for the combustion of hydrocarbonaceousfuels to produce gases having a substantially reduced soot content andthus eliminate the need for expensive soot-removal facilities. It isalso an object of the invention to increase the efficiency of thepartial combustion process by ensuring that substantially all the carboncontent of the hydrocarbonaceous fuels combusted is converted into morevaluable carbon monoxide.

The presence of soot in the hot gases produced by the partial combustionof hydrocarbonaceous fuels provides difficulties with regard to therecovery of heat from the gases. It is not generally possible to useheat exchangers of the normal straight flame tube type sinceconsiderable deposits of soot are formed on the inside walls of thetubes and thus greatly reduce the heat transfer coefficient. It ispossible to use a heat exchanger of the helical tube type, but such heatexchangers are expensive and are unsuitable for high pressure steamgeneration due to the possibility of tube collapse owing to smallunroundness of the tubes. Unroundness of a tube signifies its deviationfrom perfect radial and axial symmetry. It is therefore another objectof the present invention to produce gases having a substantially reducedsoot content; the recovery of heat from which can be carried out withnormal straight tube heat exchangers producing high pressure steam.

SUMMARY OF THE INVENTION It has now been found that in a process for thegeneration of a hydrogen and carbon monoxide-containing gas mixture bythe partial combustion of a hydrocarbonaceous fuel with anoxygen-containing gas (e.g., oxygen, air, or oxygen-enriched air) in thepresence of steam in a partial combustion zone, that the soot content ofthe resulting crude gas mixture can be substantially reduced by passingthe gas mixture containing soot in particulate form into asoot-conversion zone maintained at substantially the same elevatedtemperature and pressure as that of the partial combustion zone, andretarding the passage of the soot particles through said soot-conversionzone for at least 5 seconds, e.g., from 5 to 50 seconds. It has beenfound that if the soot particles are retained in the soot-conversionzone for this length of time, they are substantially converted intocarbon monoxide by reaction with steam and/or carbon dioxide which isalso present in the crude gas mixture. By practice of the invention itis possible to reduce the soot content of the crude gas mixture fromamounts of from 2 to 5 percent by weight or higher down to below 1percent by weight, and generally below 0.3 percent by weight. Thissubstantial reduction in in soot concentration correspondingly reducesor eliminates the need for downstream soot removal facilities andpermits the use of conventional straight tube heat exchangers toabstract heat from the hot crude gas mixture, instead of more expensivehelical coil heat exchangers which are commonly employed in thisservice. In addition, the conversion of the carbon to carbon monoxide inthe soot conversion zone increases the calorific value of the gasesproduced.

DETAILED DESCRIPTION OF THE INVENTION In processes for the partialcombustion of hydrocarbonaceous fuels which have so far been proposed,the average residence time of the soot particles in the hot gases isvery small because the gases are either immediately quenched with wateror immediately passed to a heat exchanger as soon as they pass out ofthe reactor. Accordingly the soot particles are not allowed sufficienttime for further reaction at high temperature. In the present process,however, the gases passing out of the reactor enter a soot-conversionzone in which the passage of soot particles, but not of gases, isretarded. This has the effect of increasing the residence time duringwhich the soot particles are in contact with the hot reactor gases. Thesoot particles are thus allowed sufficient time in which they can reactwith steam and/or carbon dioxide in the gases at high temperature andpressure to form carbon monoxide. The reaction is believed to proceedaccording to the following equations:

The relative proportions of steam and carbon dioxide present in thepartially combusted gases is not critical. It is only required that thecombined steam and carbon dioxide concentrations be stoichiometricallysufficient to effect conversion of the free carbon to carbon monoxide inaccordance with the above equations.

The operation of the soot-conversion zone can therefore be seen tocomprise firstly retarding the passage of soot particles and secondly toallow sufficient time for conversion of the particles so retarded intocarbon monoxide. The advantage of this operation is two-fold. Firstly itenables the production of substantially sootreduced gases, and secondlyit allows substantial conversion of the carbon content of thehydrocarbonaceous fuel into carbon monoxide, thus increasing thecalorific value of the gases produced as previously mentioned.

In general, the retardation and conversion of the soot particles in thesoot-conversion zone is such that the percentage by weight of sootparticles present in the gases leaving said zone is reduced to less than1 percent. Preferably, however, the percentage by weight of sootparticles present in the gases leaving said zone is reduced to less than0.3 percent.

It is important that the soot particles are sufficiently retarded in thesoot-conversion zone that their residence time therein allowssubstantial conversion to carbon monoxide to take place. Accordingly,the soot particles suitably remain in the soot-conversion zone for atleast 5 seconds. It is, however, preferred that the time that the sootparticles remain in the soot-conversion zone is between 15 and 50seconds.

Retardation of the soot particles is suitably effected by asoot-conversion zone consisting of at least one bed of ceramic materialor any equivalent material which is resistant to high temperatures. Ingeneral, any ceramic material capable of resisting the high temperaturespresent in the soot-conversion zone, e.g., l,O-l,600C or higher, can beemployed. Ceramic materials having the requisite refractory propertiesare known to those skilled in this art and are described, for example,in Encyclopedia of Chemical Technology by Kirk and Othmer, SecondEdition, 1968, Vol. 4, pages 762775. Suitable ceramic materials includevarious carbides, e.g., the carbides of silicon, boron, zirconium,hafnium, tantalum, vanadium, molybdenum, tungsten and niobium; variousaluminum silicates, particularly sillimanite and Korund (a specialalumina refractory material containing at least 95 percent alumina);various borides, nitrides and sulfides of high melting point metals, andvarious oxides such asmullite, zircon and the like. The soot particlesadhere to the surface of the ceramic material under the influence of Vander Waals-type forces.

The bed of ceramic material advantageously consists of packed perforatedbricks. The bricks are preferably packed on top of one another in layerssuch that the perforations of the bricks in a lower layer interconnectwith the perforations of the bricks in an upper layer. In this way theinterconnecting perforations form elongated tubes in the direction ofgas flow within the sootconversion zone. The gases pass through theelongated tubes but the soot particles adhere to the walls thereof andare therefore retarded. The perforated bricks are preferably made fromKorund, carbides or sillimanite, although they may be made from anyother suitable ceramic material which can resist high gas temperatures.The diameter of the elongated tubes may vary over a wide range. However,it should be sufficiently large such that deposition of soot particlesdoes not restrict the flow of gasesunduly and sufficiently small suchthat a large surface area of ceramic material is afforded for sootadhesion and these factors therefore dictate that the diameterpreferably is between 0.5 cm and 2.5 cm. The surface area of theelongated tubes for gas contact may also vary considerably. Preferablythe surface area is between 30 square mete rs and 200 square meters percubic meter of perforated bricks. The average gas velocity through theelongated tubes is not critical, but in general lies between 1 meter persecond and meters per second.

The ash particles in the hot gases, as in the case of the sootparticles, are temporarily retarded in the sootconversion zone. However,unlike the soot particles they do not react further with the hot gasesbut pass through the said zone unchanged. A very small proportion of theash particles however is retained within the soot-conversion zone andthus a gradual build-up of ash particles therein occurs. This build-upis accelerated if the ash content of the hydrocarbonaceous fuel is high.This eventually leads to plugging of the perforations of the bricks andinefficient soot conversion. Accordingly, after a shorter or longerperiod of operation it is necessary to remove the old bricks from thesoot-conversion zone and install new ones. The intervals betweensuccessive brick renewal periods depend to a large extent on the ashcontent of the hydrocarbonaceous fuel combusted, but in general arebetween 1 month and 12 months. In order to ensure continuous operationof the soot-conversion zone a swing reactor system is suitably utilized,whereby while a bed of bricks in one reactor is being replaced, anotherbed of bricks in another reactor is in operation.

In another embodiment of the present invention, the bed of ceramicmaterial suitably consists of at least one fluid bed of ceramicparticles. The particles are made from any suitable ceramic material andin particular from Korund, carbides or sillimanite. The diameter of theparticles may vary over a wide range, but as in the case of perforatedbricks, consideration of gas flow rate through the bed and surface areafor gas contact requires the diameter to be in general between 10 and1,000 microns. The superficial velocity of the gases passing through thefluid bed preferably lies between 0.1 and 1 meter per second, althoughoperation above and below these figures is quite possible.

During operation a certain proportion of the ash particles in the hotgases is permanently retained in the fluidized bed of ceramic particles.A gradual build-up of ash particles therefore occurs and this build-upoccurs more rapidly if the ash content of the hydrocarbonaceous fuelscombusted is high. Accordingly, after a given period of operation it isnecessary to replace the old ash-containing particles with freshparticles. The intervals between successive bed replacements in genera]are between 2 months and 20 months. A swing reactor system may suitablybe employed. Alternatively continuous addition of fresh particles andwithdrawal of ash-containing particles may be effected in order toprovide continuous operation of the soot-conversion zone so thatintermittent bed replacement is not necessary.

The temperature and pressure at which soot conversion in thesoot-conversion zone takes place are substantially the same as thetemperature and pressure at which partial combustion occurs. Thepressure in the partial combustion zone can be from 1 to 300atmospheres, but'preferably is between 10 and 150 atmospheres. Thetemperature within the partial combustion zone is, in general, fromabout 1,000C to about 1,600C, but preferably from 1,300C to 1,500C.These same ranges of pressure and temperature apply to the sootconversion zone.

A considerable advantage of the present invention lies in the fact thatthe production of substantially sootreduced gases greatly simplifies andfacilitates the subsequent heat recovery operation therefrom. In caseswhere the soot content of the gases is negligible, it is possible torecover heat from the gases in a conventional straight tube type heatexchanger since soot deposition on the inside walls of the tubes nolonger occurs. Thus the more expensive helical tube heat exchangers areno longer necessary and also heat recovery at higher steam pressuresbecomes possible, since conventional straight-tube exchangers canoperate at higher pressures than helical tube exchangers. Hence,

- cheaper equipment can be used and more efficient heat nevertheless bedesirable to use a helical gastube heat exchanger.

Any suitable hydrocarbonaceous or carbonaceous fuel may be partiallycombusted according to the present invention including natural gas,heavy oils, coal, coke and shale oil, tar sands oil, etc. In general thefuel will be a liquid hydrocarbon fuel. If a solid fuel is employed, itmay be combusted in either a dry pulverized form or in a slurry withliquid.

The invention also relates to an apparatus suitable for carrying out theprocess described hereinbefore. This apparatus comprises:

(a) a brick-lined partial combustion reactor free of internals andsolids with an inlet for fuel, oxygencontaining gas and steam, and anoutlet for discharging partially combusted, soot particlecontaininggases, and

(b) a soot-conversion vessel connected to the partial combustion reactorcontaining a bed of ceramic material of sufficient thickness andporosity to retard passage of the soot particles through said sootconversion vessel for at least 5 seconds whereby the soot particles aresubstantially converted to carbon monoxide, said soot-conversion vesselhaving an inlet for the partially combusted, sootcontaining gases fromthe partial combustion reactor, and an outlet through which thesoot-reduced gases are discharged from the soot-conversion vessel.

In a preferred embodiment, the outlet of the sootconversion vessel isconnected to a waste heat boiler. The waste heat boiler is suitably ofthe conventional straight tube type if the gases leaving thesootconversion vessel contain negligible amounts of soot. If smallamounts of soot are still present in the gases then a helical tube typeheat exchanger may be employed.

The number of beds of ceramic material contained within thesoot-conversion vessel is not of critical importance. Accordingly anynumber of separate beds, within reason, may be contained within thesootconversion vessel although one single bed is preferred. The bed(s)of ceramic material must be of sufficient porosity to permit the passageof the gases therethrough while retaining the soot particles for theprescribed length of time to effect their conversion to carbon monoxide,i.e., at least 5 seconds.

According to one embodiment of the invention the soot-conversion vesselcontains a bed of packed perforated bricks. The perforated bricks arepacked on top of one another in layers such that the perforations in thebricks in a lower layer interconnect with the perforations of the bricksin an upper layer. In this way the interconnecting perforations formelongated tubes in the direction of gas flow within the soot-conversionvessel. The total length of the elongated tubes formed by the packedperforated bricks varies according to, inter alia, the surface arearequired for soot retardation, the diameter of the perforations and thesoot content of the combustion gases entering the sootconversion zone,but in general is between 0.5 and 5 meters. The surface area of theelongated tubes suitably lies between square meters and 200 squaremeters per cubic meter of the packed perforated bricks.

The number of layers of perforated bricks within the soot-conversionzone depends on the length of elongated tubes required and the size ofthe individual bricks but advantageously lies between 2 and 100. The

long, 5 cm wide and 5 cm deep and 60 cm long, 20 cm wide and 20 cm deep.The number of perforations per brick suitably lies between 5 and 750,and the diameter of the perforations between 0.5 cm and 2.5 cm.

In another embodiment, the soot conversion vessel contains at least onebed of fluidizable particles. The size of the particles is not criticalbut advantageously the average diameter thereof is between 10 and 1000microns.

A method in which the process and apparatus according to the presentinvention are suitably used for the partial combustion ofhydrocarbonaceous fuels to produce substantially soot-reduced gases isdescribed below with reference to the accompanying drawings, by way ofexample and without limitation.

FIG. 1 is a diagrammatic representation of an apparatus for the partialcombustion of hydrocarbonaceous fuels to produce substantiallysoot-reduced gases.

FIG. 2 is a partially cutaway, perspective view of a perforated ceramicbrick suitable for use in the sootconversion vessel.

With regard to FIG. 1, hydrocarbonaceous fuel is introduced via line 1and oxygen is introduced via line 2 into burner part 3 of partialcombustion reactor 4. Steam if required may be introduced via both lines1 and 2. The hot combustion gases pass through a con necting piece 5which connects the reactor to sootconversion vessel 6. The lattercontains a bed of ceramic material 7 through which the hot combustiongases pass in upflow. The bed of ceramic material can suitably compriseceramic bricks as shown in FIG. 2, consisting of ceramic material 13 andhaving perforations 14 through which the soot-containing combustiongases flow, the soot particles adhering to the inside surfaces of theperforations thus retarding their passage and permitting theirconversion to carbon monoxide. The gases leaving the top of thesoot-conversion vessel enter heat exchanger 8 via line 9 and leave theheat exchanger via line 10. Water enters the heat exchanger via line 11and steam leaves via line 12.

In a practical embodiment of the invention, a liquid hydrocarbon fuelmay be combusted in the presence of oxygen and steam in a reactor andthe combustion gases passed at a temperature of I,400C and a pressure of60 atmospheres from the reactor to a sootconversion vessel containing abed of packed perforated ceramic bricks. The combustion gases enteringthe soot-conversion vessel contain 3 percent by weight of sootparticles.

The bed is packed with perforated bricks having dimensions of 36centimeters long, 12 centimeters wide and 10 centimeters deep and theheight and diameter of the packed bed are 2 meters and 1.4 meters,respectively. Each brick contains 50 perforations of 1.5 centimetersdiameter and the surface area of the tubes formed by the interconnectingperforations is square meters per cubic 'meter of packed bricks.

If the volume flow rate of the combustion gases flowing through thesoot-conversion vessel is 1.45 cubic meters per second and the averagegas flow through the tubes is 4.5 meters per second, then the averagesoot retardation time is 20 seconds and the average thickness of thesoot layer formed on the surface of the perforations of the packedbricks is 0.8 millimeters. In this case the gases passing out of thesoot conversion vessel contain 0.03 percent by weight of soot particles.Hence a 99 percent conversion of the soot particles present in the gasesentering the soot-conversion vessel is achieved.

In a further practical embodiment, a liquid hydrocarbon fuel may becombusted in the presence of oxygen and steam in a reactor and thecombustion gases passed at a temperature of 1,400C and a pressure of 60atmospheres from the reactor to a soot-conversion vessel containing afluidized bed of ceramic particles. The combustion gases entering thesoot-conversion vessel contain 3 percent by weight of soot particles and300 ppm of ash particles.

The bed consists of 9.2 cubic meters or 12 tons of Korund particleshaving an average diameter of 50 to 200 microns. The height and diameterof the fluidized bed are 2 meters and 2.4 meters respectively.

If the superficial velocity of the combustion gases flowing through thefluidized bed is 0.3 meters per second, then the soot retardation timeis greater than seconds and the gases passing out of the sootconversionvessel contain 0.03 percent by weight of soot particles. Hence a 99percent conversion of the soot particles present in the gases enteringthe soot conversion is achieved.

Operation of the process at this soot conversion level may be continuedfor 3 months until the amount of ash which builds up within thefluidized bed is 6.5 tons. At this point replacement of the bed withfresh particles is considered desirable since the bed contains about 30percent by weight of ash particles.

What is claimed is:

1. In a process for the generation of a hydrogen and carbonmonoxide-containing gas mixture by the partial combustion of ahydrocarbonaceous fuel with an oxygen-containing gas in the presence ofsteam in a partial combustion zone at a temperature of from about 1,000to about 1,600C and a pressure from 1 to 300 atmospheres whereby a crudehydrogen, steam, carbon dioxide and carbon-monoxide containing gasmixture containing contaminating amounts of soot in particulate form isobtained, the improvement which comprises substantially reducing thesoot content of the crude gas mixture by passing the gas mixture into asoot-conversion zone which contains at least one bed of ceramic materialand is maintained at substantially the same elevated temperature andpressure as that of the partial combustion zone, and retarding thepassage of the soot particles through said soot-conversion zone for atleast 5 seconds by adherence of said soot particles to said ceramicmaterial whereby the soot particles are converted to carbon monoxide byreaction of the soot particles with combined stoichiometric amounts ofsteam and carbon dioxide in the crude gas mixture, re-

ducing the soot content of the crude gas mixture to less than I percentby weight.

2. The process of claim 1 wherein the pressure in the partial combustionzone is between 10 and atmospheres.

3. The process of claim 2 wherein the time that the soot particlesremain in the soot-conversion zone is between 15 and 50 seconds.

4. The process of claim 1 wherein the bed of ceramic material throughwhich the crude gas mixture is flowed comprises layers of perforatedbricks, the perforations of the bricks in each lower layerinterconnecting with the perforations of adjoining upper layers to formelongated tubes in the direction of gas flow.

5. The process of claim 1 wherein the bed of ceramic material throughwhich the crude gas mixture is flowed comprises a fluid bed of ceramicparticles.

6. The process of claim 4 wherein the temperature of the gases in thepartial combustion zone is from 1,300C to 1,500C and the soot content ofthe gases leaving the soot-conversion zone is less than 0.3 percent byweight.

7. The process of claim 5 wherein the average diameter of the ceramicparticles is between 10 and 1,000 microns.

, 8. The process of claim 6 wherein the diameter ofthe elongated tubesthrough which the crude gas mixture flows is between 0.5 cm and 2.5 cmand the surface area of the elongated tubes is between 30 square metersand 200 square meters per cubic meter of said bricks.

9. The process of claim 7 wherein the superficial velocity of the gasespassing through the fluid bed lies between 0.1 and 1 meter per second.

10. A process of claim 9 wherein the temperature of the gases in thepartial combustion zone are from l,300 to 1,500C and the soot content ofthe gases leaving the soot conversion zone is less than 0.3% by weight.

1. IN A PROCESS FOR THE GENERATION OF A HYDROGEN AND CARBONMONOXIDE-CONTAINING GAS MIXTURE BY THE PARTIAL COMBUSTION OF AHYDROCARBONACEOUS FUEL WITH AN OXYGEN-CONTAINING GAS IN THE PRESENCE OFSTEAM IN A PARTIAL COMBUSTION ZONE AT A TEMPERATURE OF FROM ABOUT 1,000*TO ABOUT 1,600*C AND A PRESSURE FROM 1 TO 300 ATOMOSPHERE WHEREBY ACRUDE HYDROGEN, STEAM, CARBON DIOXIDE AND CARBON-MONOXIDE CONTAINING GASMIXTURE CONTAINING CONTAMINATING AMOUNTS OF SOOT IN PARTICULATE FORM ISOBTAINED, THE IMPROVEMENT WHICH COMPRISES SUBSTANTIALLY REDUCING THESOOT CONTENT OF THE CRUDE HYDROGEN, STEAM THE GAS MIXTURE INTO ASOOT-CONVERSION ZONE WHICH CONTAINS AT LEAST ONE BED OF CERAMIC MATERIALAND IS MAINTAINED AT SUBSTANTIALLY THE SAME ELEVATED TEMPERATURE ANDPRESSURE AS THAT OF THE PARTIAL COMBUSTION ZONE, AND RETARDING THEPASSAGE OF THE SOOT PARTICLES THROUGH SAID SOOT-CONVERSION ZONE FOR ATLEAST 5 SECONDS BY ADHERENCE OF SAID SOOT PARTICLES OF SAID CERAMICMATERIAL WHEREBY THE SOOT PARTICLES ARE CONVERTED TO CARBON MONOXIDE BYREACTION OF THE SOOT PARTICLES WITH COMBINED STOICHIOMETRIC AMOUNTS OFSTEAM AND CARBON DIOXIDE IN THE CRUDE GAS MIXTURE, REDUCING THE SOOTCONTENT OF THE CRUDE GAS MIXTURE TO LESS THAN 1 PERCENT BY WEIGHT. 2.The process of claim 1 wherein the pressure in the partial combustionzone is between 10 and 150 atmospheres.
 3. The process of claim 2wherein the time that the soot particles remain in the soot-conversionzone is between 15 and 50 seconds.
 4. The process of claim 1 wherein thebed of ceramic material through which the crude gas mixture is flowedcomprises layers of perforated bricks, the perforations of the bricks ineach lower layer interconnecting with the perforations of adjoiningupper layers to form elongated tubes in the direction of gas flow. 5.The process of claim 1 wherein the bed of ceramic material through whichthe crude gas mixture is flowed comprises a fluid bed of ceramicparticles.
 6. The process of claim 4 wherein the temperature of thegases in the partial combustion zone is from 1,300*C to 1,500*C and thesoot content of the gases leaving the soot-conversion zone is less than0.3 percent by weight.
 7. The process of claim 5 wherein the averagediameter of the ceramic particles is between 10 and 1,000 microns. 8.The process of claim 6 wherein the diameter of the elongated tubesthrough which the crude gas mixture flows is between 0.5 cm and 2.5 cmand the surface area of the elongated tubes is between 30 square metersand 200 square meters per cubic meter of said bricks.
 9. The process ofclaim 7 wherein the superficial velocity of the gases passing throughthe fluid bed lies between 0.1 and 1 meter per second.
 10. A process ofclaim 9 wherein the temperature of the gases in the partial combustionzone are from 1,300* to 1,500*C and the soot content of the gasesleaving the soot conversion zone is less than 0.3% by weight.